Function and pathomechanics of the sacroiliac joint. A review.
The purpose of this article is to describe the biomechanics and function of the sacroiliac joint, the dysfunction and pathomechanics of the sacroiliac joint as a common cause of low back pain, a simple assessment procedure, associated pain mechanisms, treatment and prevention of the problem, and a discussion of related literature. The sacroiliac joints are essentially nonweight-bearing joints that function to absorb forces from various directions. The common onset of dysfunction is during trunk flexion when a person is standing without adequate support of the anterior pelvis. The anterior shift of the weight of the upper trunk causes the innominates to rotate anteriorly and downward and become fixed on the sacrum. Movement downward of the acetabula in relationship to the sacroiliac joint not only results in biomechanical changes but causes the legs to appear longer than they actually are. Physical therapists can correct the dysfunction by manually rotating the innominates posteriorly on the sacrum while they observe objective changes in apparent leg length. People can prevent this dysfunction through adequate anterior pelvic support when they lean forward. Some possible consequences of untreated sacroiliac dysfunction are also discussed.